Inverse atmospheric transport modelling using the open-source FREAR tool

An inverse modelling tool has been developed with the initial purpose of improving the verification of the Comprehensive Nuclear-Test-Ban Treaty. The tool is able to make inferences of source parameters (such as source location and release amount) given a set of airborne activity concentrations and their corresponding source-receptor-sensitivities obtained from atmospheric transport and dispersion modelling. The tool features several independent methods to perform the inverse modelling, including Bayesian inference and cost function optimisation. The tool can digest instrumental detections and non-detections and can take into account the possibility of misses and false alarms. An ensemble of atmospheric transport modelling can be provided for more rigorous estimation of the model uncertainty. Lastly, the tool features a flexible source parameterization, as demonstrated by the fact that it has also been used to study the amount of Cs-137 released during resuspension from the wildfires in the Chernobyl Exclusion Zone in April 2020. In this poster contribution, an overview of the open-source FREAR (Forensic Radionuclide Event Analysis and Reconstruction) tool will be presented and specific features will be highlighted.